Semiconductor device including protection circuit and switch circuit and its testing method

ABSTRACT

In a semiconductor device including a semiconductor element to be protected having first and second electrodes, and a protection circuit coupled between the first and second electrodes, a switch circuit is inserted between the first and second electrodes in series to the protection circuit. The switch circuit is turned ON by such a voltage that turns ON the semiconductor element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device including a semiconductor element with a protection circuit and its testing method.

2. Description of Related Art

In a prior art semiconductor device including a semiconductor element so-called a gate-insulating-type transistor such as a power MOS transistor and an insulated gate bipolar transistor (IGBT), if an excessive voltage is applied to the gate of the gate-insulating-type transistor, the gate insulating layer thereof would be electrostatically destroyed. Therefore, in order to prevent the gate insulating layer from being electrostatically destroyed, a protection circuit is connected between the gate and source of the gate-insulating-type transistor to clamp the difference in voltage thereof.

The protection circuit is constructed by one or more diodes, and has an anode connected to an anode pad and a cathode connected to a source pad of the gate-insulating-type transistor. The anode pad is connected by a bonding wire to a gate pad of the gate-insulating-type transistor. On the other hand, in order to remove semiconductor devices with low gate breakdown voltages, a gate breakdown voltage test operation is carried out in a wafer state before bonding the bonding wire. In this case, a predetermined test voltage is applied to the gate of a gate-insulating-type transistor to determine whether or not the gate-insulating-type transistor is normally operated.

The above-described prior art semiconductor device is disclosed in Japanese Unexamined Patent Publication (Kokai) No. P2005-175054 A. This will be explained later in detail.

However, the inventor has recognized that, since the anode pad whose size is very large, is required for the protection circuit, the above-described prior art semiconductor device becomes large in size, which would increase the manufacturing cost.

SUMMARY

The present invention seeks to solve the above-described problem.

In one embodiment, in a semiconductor device including a semiconductor element to be protected having first and second electrodes, and a protection circuit coupled between the first and second electrodes, a switch circuit is inserted between the first and second electrodes in series to the protection circuit. The switch circuit is turned ON by such a voltage that turns ON the semiconductor element.

Thus, a pad specialized for the protection circuit would be unnecessary.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages and features of the present invention will be more apparent from the following description of certain preferred embodiments as compared with the prior art, taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a circuit diagram illustrating a prior art semiconductor device;

FIG. 2 is a detailed circuit diagram of the semiconductor device of FIG. 1 in a gate breakdown voltage test mode;

FIG. 3 is a circuit diagram illustrating a first embodiment of the semiconductor device according to the present invention;

FIG. 4 is a detailed circuit diagram of the semiconductor device of FIG. 3 in a gate breakdown voltage test mode;

FIG. 5 is a circuit diagram illustrating a modification of the semiconductor device of FIG. 3;

FIG. 6 is a detailed circuit diagram of the semiconductor device of FIG. 5 in a gate breakdown voltage test mode;

FIG. 7 is a circuit diagram illustrating a second embodiment of the semiconductor device according to the present invention;

FIG. 8 is a detailed circuit diagram of the semiconductor device of FIG. 7 in a gate breakdown voltage test mode;

FIG. 9 is a circuit diagram illustrating a modification of the semiconductor device of FIG. 7;

FIG. 10 is a detailed circuit diagram of the semiconductor device of FIG. 9 in a gate breakdown voltage test mode;

FIGS. 11A and 11B are circuit diagrams illustrating other modifications of the semiconductor devices of FIGS. 3 and 7, respectively;

FIGS. 12A and 12B are circuit diagrams further illustrating other modifications of the semiconductor devices of FIGS. 3 and 7, respectively;

FIGS. 13A and 13B are circuit diagrams further illustrating still other modifications of the semiconductor devices of FIGS. 3 and 7, respectively; and

FIGS. 14A and 14B are circuit diagrams illustrating third and fourth embodiments of the semiconductor device according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Before describing the present invention, the prior art will be explained in detail with reference to FIGS. 1 and 2 in order to facilitate the understanding of the present invention (see: FIGS. 1 and 2 of Japanese Unexamined Patent Publication (Kokai) No. P2005-175054 A).

In FIG. 1, a semiconductor device (chip) 1 is constructed by an n-channel MOS transistor 11 n and a protection circuit 12 formed by one diode or two or more serially-connected diodes to clamp the difference in voltage between a gate and source of the n-channel MOS transistor 11 n. For example, if the number of diodes in the protection circuit 12 is four, a clamp voltage is four times the forward voltage of one diode.

The n-channel MOS transistor 11 n has a drain connected to a drain pad P_(D). Also, the gate is connected to a gate pad P_(G), and the source is connected to a source pad P_(S).

The protection circuit 12 has an anode connected to an anode pad P_(A) and a cathode connected to the source pad P_(S).

The semiconductor device 1 is mounted on a board (motherboard or interposer) on which external terminals T₁, T₂ and T₃ are provided.

The anode pad P_(A) is connected by a bonding wire W₀ to the gate pad P_(G). Also, the drain pad P_(D), the gate pad P_(G) and the source pad P_(S) are connected by bonding wires W₁, W₂ and W₃ to the external terminals T₁, T₂ and T₃, respectively.

Thus, the protection circuit 12 is connected between the gate and source of the n-channel MOS transistor 11 n. Therefore, even when an excessive voltage higher than the clamp voltage of the protection circuit 12 is applied between the gate pad P_(G) and the source pad P_(S), the protection circuit 12 is in a conductive state, thus preventing the gate insulating layer of the n-channel MOS transistor 11 n from being electrostatically destroyed.

A gate breakdown voltage test operation is performed upon the semiconductor device 1 of FIG. 1 which is in a wafer state as illustrated in FIG. 2. In FIG. 2, the bonding wires W₀, W₁, W₂ and W₃ of FIG. 1 are not provided, and test probes TP_(G) and TP_(S) are in contact with the gate pad P_(G) and the source pad P_(S), respectively. Thus, since the protection circuit 12 is not connected to the gate of the n-channel MOS transistor 11 n, the protection circuit 12 is invalidated. In this state, a test voltage can be applied between the probes TP_(G) and TP_(S) without consideration of the clamp voltage of the protection circuit 12.

After the gate breakdown voltage test operation has been completed, the semiconductor device 1 of FIG. 2 is diced and mounted on a board, and then, a bonding operation is performed thereupon to obtain the semiconductor device 1 of FIG. 1.

In the semiconductor device 1 of FIG. 1, however, since the anode pad P_(A) whose size is about 100 μm×100 μm, for example, is required, the semiconductor device 1 of FIG. 1 becomes large in size, which would increase the manufacturing cost.

In FIG. 3, which illustrates a first embodiment of the semiconductor device according to the present invention, the anode pad P_(A) and the bonding wire W₀ of FIG. 1 are replaced by a switch circuit 13, to form a semiconductor device 2. That is, the switch circuit 13 is connected between the gate of the n-channel MOS transistor 11 n and the anode of the protection circuit 12.

The switch circuit 13 is constructed by a p-channel MOS transistor 131 p connected between the gate of the n-channel MOS transistor 11 n and the anode of the protection circuit 12, a fuse 132 connected between the source and gate of the p-channel MOS transistor 131 p, and a resistor 133 serving as a pull-down resistor connected between the gate of the p-channel MOS transistor 131 p and the source of the n-channel MOS transistor 11 n (the cathode of the protection circuit 12).

In FIG. 3, the fuse 132 is melted. Note that the fuse 132 is a laser-melted fuse which does not require a melting current (voltage) pad.

Thus, even when an excessive voltage higher than the clamp voltage of the protection circuit 12 is applied between the gate pad P_(G) and the source pad P_(S), the source-to-gate voltage of the p-channel MOS transistor 131 p is increased to turn ON the p-channel MOS transistor 131 p, so that the protection circuit 12 is in a conductive state, thus preventing the gate insulating layer of the n-channel MOS transistor 11 n from being electrostatically destroyed.

A gate breakdown voltage test operation is performed upon the semiconductor device 2 of FIG. 3 which is in a wafer state as illustrated in FIG. 4. In FIG. 4, the bonding wires W₁, W₂ and W₃ of FIG. 3 is not provided and the fuse 132 is not melted. Also, test probes TP_(G) and TP_(S) are in contact with the gate pad P_(G) and the source pad P_(S), respectively. Thus, since the p-channel MOS transistor 131 p is turned OFF, the protection circuit 12 is invalidated. In this state, a test voltage can be applied between the probes TP_(G) and TP_(S) without consideration of the clamp voltage of the protection circuit 12.

After the gate breakdown voltage test operation has been completed, the fuse 132 is melted by laser trimming. The semiconductor device 2 of FIG. 4 is diced and mounted on a board, and then, a bonding operation is performed thereupon to obtain the semiconductor device 2 of FIG. 3.

In the semiconductor device 2 of FIG. 3, since the anode pad P_(A) of FIG. 1 is not required, the semiconductor device 2 of FIG. 3 becomes small in size, which would decrease the manufacturing cost.

In FIG. 5, which illustrates a modification of the semiconductor device 2 of FIG. 3, a fuse 134 is added to the switch circuit 13 of FIG. 3. The fuse 134 is connected in parallel with the protection circuit 12.

Even in FIG. 5, the fuse 134 is melted. Note that the fuse 134 is also a laser-melted fuse which does not require a melting current (voltage) pad.

A gate breakdown voltage test operation is performed upon the semiconductor device 2 of FIG. 5 which is in a wafer state as illustrated in FIG. 6. In FIG. 6, the bonding wires W₁, W₂ and W₃ of FIG. 5 are not provided and the fuses 132 and 134 are not melted. Also, test probes TP_(G) and TP_(S) are in contact with the gate pad P_(G) and the source pad P P_(S), respectively. Thus, since the p-channel MOS transistor 131 p is turned OFF, the protection circuit 12 is invalidated. In this state, a test voltage is applied so that a leakage current I_(LK) may flow through the p-channel MOS transistor 131 p as indicated in FIG. 6. Even in this case, the leakage current I_(LK) flows through the fuse 134, not the protection circuit 12. As a result, such a test voltage can be applied between the probes TP_(G) and TP_(S) without consideration of the clamp voltage of the protection circuit 12.

After the gate breakdown voltage test operation, the fuse 134 together with the fuse 132 is trimmed by laser.

In FIG. 7, which illustrates a second embodiment of the semiconductor device according to the present invention, the anode of the protection circuit 12 of FIG. 3 is connected to the gate of the n-channel MOS transistor 11 n, and the switch circuit 13 of FIG. 3 is replaced by a switch circuit 14, to form a semiconductor device 3. That is, the switch circuit 14 is connected between the cathode of the protection circuit 12 and the source of the n-channel MOS transistor 11 n.

The switch circuit 14 is constructed by a p-channel MOS transistor 141 p connected between the cathode of the protection circuit 12 and the source of the n-channel MOS transistor 11 n, a fuse 142 connected between the anode of the protection circuit 12 and the gate of the p-channel MOS transistor 141 p, and a resistor 143 serving as a pull-down resistor connected between the gate and drain of the p-channel MOS transistor 141 p.

In FIG. 7, the fuse 142 is melted. Note that the fuse 142 is a laser-melted fuse which does not require a melting current (voltage) pad.

Thus, even when an excessive voltage higher than the clamp voltage of the protection circuit 12 is applied between the gate pad P_(G) and the source pad P_(S), the source-to-gate voltage of the p-channel MOS transistor 141 p is increased to turn ON the p-channel MOS transistor 141 p, so that the protection circuit 12 is in a conductive state, thus preventing the gate insulating layer of the n-channel MOS transistor 11 n from being electrostatically destroyed.

A gate breakdown voltage test operation is performed upon the semiconductor device 3 of FIG. 7 which is in a wafer state as illustrated in FIG. 8. In FIG. 8, the bonding wires W₁, W₂ and W₃ of FIG. 7 are not provided and the fuse 142 is not melted. Also, test probes TP_(G) and TP_(S) are in contact with the gate pad P_(G) and the source pad P_(S), respectively. Thus, since the p-channel MOS transistor 141 p is turned OFF, the protection circuit 12 is invalidated. In this state, a test voltage can be applied between the probes TP_(G) and TP_(S) without consideration of the clamp voltage of the protection circuit 12.

After the gate breakdown voltage test operation has been completed, the fuse 142 is melted by laser trimming. The semiconductor device 3 of FIG. 8 is diced and mounted on a board, and then, a bonding operation is performed thereupon to obtain the semiconductor device 3 of FIG. 7.

In the semiconductor device 3 of FIG. 7, since the anode pad P_(A) of FIG. 1 is not required, the semiconductor device 3 of FIG. 7 becomes small in size, which would decrease the manufacturing cost.

In FIG. 9, which illustrates a modification of the semiconductor device 3 of FIG. 7, a fuse 144 is added to the switch circuit 14 of FIG. 7. The fuse 144 is connected in parallel with the protection circuit 12.

Even in FIG. 9, the fuse 144 is melted. Note that the fuse 144 is also a laser-melted fuse which does not require a melting current (voltage) pad.

A gate breakdown voltage test operation is performed upon the semiconductor device 3 of FIG. 9 which is in a wafer state as illustrated in FIG. 10. In FIG. 10, the bonding wires W₁, W₂ and W₃ of FIG. 9 are not provided and the fuses 142 and 144 are not melted. Also, test probes TP_(G) and TP_(S) are in contact with the gate pad P_(G) and the source pad P_(S), respectively. Thus, since the p-channel MOS transistor 141 p is turned OFF, the protection circuit 12 is invalidated. In this state, a test voltage is applied so that a leakage current I_(LK) may flow through the p-channel MOS transistor 141 p as indicated in FIG. 10. Even in this case, the leakage current I_(LK) flows through the fuse 144, not the protection circuit 12. As a result, such a test voltage can be applied between the probes TP_(G) and TP_(S) without consideration of the clamp voltage of the protection circuit 12.

After the gate breakdown voltage test operation, the fuse 144 together with the fuse 142 is trimmed by laser.

In the semiconductor devices 2 and 3 of FIGS. 3 to 10, the size of the switch circuits 13 and 14 is smaller than that of the anode pad P_(A) of FIG. 1. For example, the size of the p-channel MOS transistor 131 p (141 p) is about 5 μm×50 μm (=250 μm²) and the size of the resistor 133 (143) is about 1 μm×5 μm (=5 μm²). Also, since connections serve as the fuses 132 and 134 (142 and 144), the size of the fuses 132 and 134 (142 and 144) is trivial. Therefore, the size of the switch circuit 13 (14) is about 300 μm², while the size of the anode pad P_(A) of FIG. 1 is 10000 μm². Thus, the size of the semiconductor devices 2 and 3 of FIGS. 3 to 10 is much smaller than that of the semiconductor device 1 of FIGS. 1 and 2.

In the semiconductor devices 2 and 3 of FIGS. 3 to 10, the transistor 11 n is of an n-type and the transistors 131 p and 141 p are of a p-type. The transistors 131 p and 141 p can be replaced by n-channel MOS transistors 131 n and 141 n, respectively, as illustrated in FIGS. 11A and 11B corresponding to FIGS. 3 and 7, respectively. In FIGS. 11A and 11B, the switch circuits 13 and 14 of FIGS. 3 and 7 are replaced by switch circuits 13′ and 14′, respectively, where the transistor 131 n (141 n) is provided instead of the transistor 131 p (141 p), and the fuse 132 (142) and the resistor 133 (143) are exchanged with each other.

In FIGS. 11A and 11B, note that fuses 134 and 144 can be added to the switch circuits 13′ and 14′, respectively.

Also, the transistor 11 n can be replaced by a p-channel MOS transistor 11 p as illustrated in FIGS. 12A and 12B corresponding to FIGS. 3 and 7, respectively. In FIGS. 12A and 12B, the semiconductor devices 2 and 3 of FIGS. 3 and 7 are replaced by semiconductor devices 2′ and 3′, respectively, where the transistor 11 p is provided instead of the transistor 11 n of FIGS. 3 and 7.

In FIGS. 12A and 12B, note that fuses 134 and 144 can be added to the switch circuits 13 and 14, respectively.

Further, the transistors 131 p and 141 p can be replaced by n-channel MOS transistors 131 n and 141 n, respectively, and also, the transistor 11 n can be replaced by a p-channel MOS transistor 11 p, as illustrated in FIGS. 13A and 13B corresponding to FIGS. 3 and 7, respectively. In FIGS. 13A and 13B, the semiconductor devices 2 and 3 of FIGS. 3 and 7 are replaced by semiconductor devices 2″ and 3″, respectively, where the transistor 11 p is provided instead of the transistor 11 n of FIGS. 3 and 7, and the switch circuits 13 and 14 of FIGS. 3 and 7 are replaced by switch circuits 13′ and 14′, respectively, where the transistor 131 n (141 n) is provided instead of the transistor 131 p (141 p), and the fuse 132 (142) and the resistor 133 (143) are changed with each other.

In FIGS. 13A and 13B, note that fuses 134 and 144 can be added to the switch circuits 13′ and 14′, respectively.

Additionally, the protection circuit 12 can be constructed by a Zener diode whose breakdown voltage serves as a clamp voltage (see: FIGS. 14A and 14B).

FIGS. 14A and 14B illustrate third and fourth embodiments, respectively, of the semiconductor device according to the present invention. That is, the switch circuits 13 (13′) and 14 (14′) of FIGS. 3 and 7 (FIGS. 11A and 11B) can be applied to a CMOS device as illustrated in FIGS. 14A and 14B, where the p-channel MOS transistor 11 p and the n-channel MOS transistor 11 n are connected in series between power supply lines V_(DD) and V_(SS). The gates of the transistors 11 p and 11 n are connected to an input line IN and the drains of the transistors 11 p and 11 n are connected to an output line OUT.

In FIGS. 14A and 14B, the switch circuits 13 and 14 are connected between the source and drain of the p-channel MOS transistor 11 p and between the source and drain of the n-channel MOS transistor 11 n.

In FIG. 14A, Zener diodes 12′ serving as protection circuits 12 of FIG. 3 are connected between the power supply line V_(DD) and the input line IN, between the input line IN and the power supply line V_(SS), between the power supply line V_(DD) and the output line OUT, and between the output line OUT and the power supply line V_(SS). Switch circuits which are the same as the switch circuit 13 of FIG. 3 are connected to the cathodes of the Zener diodes 12′, the power supply line V_(DD) (or the power supply line V_(SS)) and the input line IN (or the output line OUT). Also, an input pad P_(IN), a power supply pad P_(VDD), output pad P_(OUT) and a power supply pad P_(VSS) are connected by bonding wires W₁₁, W₁₂, W₁₃ and W₁₄ to external terminals T₁₁, T₁₂, T₁₃ and T₁₄, respectively. Thus, a semiconductor device 4 is formed.

In FIG. 14B, Zener diodes 12′ serving as protection circuits 12 of FIG. 7 are also connected between the power supply line V_(DD) and the input line IN, between the input line IN and the power supply line V_(SS), between the power supply line V_(DD) and the output line OUT, and between the output line OUT and the power supply line V_(SS). Switch circuits which are the same as the switch circuit 14 of FIG. 7 are connected to the anodes of the Zener diodes 12′ and the power supply line V_(DD) (or the power supply line V_(SS)) and the input line IN (or the output line OUT). Also, an input pad P_(IN), a power supply pad P_(VDD), and output pad P_(OUT) and a power supply pad P_(VSS) are connected by bonding wires W₂₁, W₂₂, W₂₃ and W₂₄ to external terminals T₂₁, T₂₂, T₂₃ and T₂₄, respectively. Thus, a semiconductor device 5 is formed.

In FIGS. 14A and 14B, when a gate breakdown voltage test operation is performed upon the semiconductor devices 4 and 5 in a wafer state where the fuses 132 and 142 are not melted, test probes (not shown) are in contact with the input pad P_(IN), the power supply pad P_(VDD) and the power supply pad P_(VSS)) respectively. In this case, the transistor 131 p or 131 n is turned OFF so that the Zener diodes 12′ are invalidated. Therefore, a test voltage can be applied the pad P_(IN) to observe the breakdown voltage of the p-channel MOS transistor 11 p and the breakdown voltage of the n-channel MOS transistor 11 n. In this case, the test voltage needs to be increased or decreased within a large voltage range from 0V to 30V, for example. That is, voltages of 30V and 0V are applied to the pads P_(VDD) and P_(VSS), respectively, while the switch circuits 13 and 14 are turned OFF. Note that, if the switch circuits 13 and 14 are absent, a high voltage of 30V cannot be applied between the source and drain of the p-channel MOS transistor 11 p and between the source and drain of the n-channel MOS transistor 11 n due to the small Zener voltage of the Zener diode 12′.

Note that, in FIG. 14A, the switch circuit 13 can be replaced by the switch circuit 13′ of FIG. 11A. Also, in FIG. 14B, the switch circuit 14 can be replaced by the switch circuit 14′ of FIG. 11B.

In the above-described embodiments, the semiconductor devices 2, 2′, 2″, 3, 3′, 3″, 4 and 5 are connected by the bonding wires W₁, W₂, W₃, W₁₁, W₁₂, W₁₃, W₁₄, W₂₁, W₂₂, W₂₃ and W₂₄ to the external terminals T₁, T₂, T₃, T₁₁, T₁₂, T₁₃, T₁₄, T₂₁, T₂₂, T₂₃ and T₂₄ of a lead frame, a motherboard or an interposer. However, the present invention can be applied to a flip-chip type semiconductor device (bare chip) which is connected to solder balls of a lead frame, a motherboard or an interposer without bonding wires.

It is apparent that the present invention is not limited to the above-described embodiments, but may be modified and changed without departing from the scope and sprit of the present invention. 

1. A method for testing a semiconductor device that has a transistor to be protected, and a fuse and a protection circuit that are operative to electrically protect said transistor in a first state of said fuse and to electrically separate said protection circuit from said transistor in a second state of said fuse, said method comprising: performing a test operation upon said transistor in said second state of said fuse, changing said fuse from said second state to said first state, and wherein said second state is a conductive state.
 2. The method as set forth in claim 1, wherein said changing said fuse is carried out by blowing said fuse.
 3. The method as set forth in claim 2, wherein said blowing said fuse is carried out by using a laser.
 4. The method as set forth in claim 1, further comprising connecting by a wire an electrode of said transistor to an external terminal in said first state of said fuse.
 5. The method as set forth in claim 1, wherein: said transistor has first and second electrodes, said protection circuit is coupled between said first and second electrodes, said fuse is part of said switch circuit, which further comprises a resistive element connected between said second electrode and a circuit node, and a transistor having a source-drain current path connected in series between said first and second electrodes to said protection circuit and having a gate connected to said circuit node, said fuse is connected between said first electrode and said circuit node, and said switch circuit is disposed in series between said first and second electrodes to said protection circuit. 